U.S. officials familiar with reports of the White House hacking incident said it took place earlier this month and involved unidentified hackers, believed to have used computer servers in China, who accessed the computer network used by the White House Military Office (WHMO), the president’s military office in charge of some of the government’s most sensitive communications, including strategic nuclear commands. The office also arranges presidential communications and travel, and inter-government teleconferences involving senior policy and intelligence officials.

An Obama administration national security official said: “This was a spear phishing attack against an unclassified network.”